1. Field of the Invention
The present invention relates to a system and method for pathogen detection via culture of a biological fluid.
2. Description of the Related Art
Many medical diagnoses require that a fluid sample, such as a blood sample, be taken from a patient, cultured in a growth medium, and then examined for the presence of a pathogen believed to be causing the patient's illness. The growth medium provides nutrients that allow the pathogen, such as a bacteria, virus, mycobacteria, mammalian cells or the like, to multiply to a sufficient number so that their presence can be detected.
In some cases, the pathogen can multiply to a large enough number so that it can be detected visually. For example, a portion of the culture can be placed on a microscope slide and visually examined to detect the presence of a pathogen of interest.
Alternatively, the presence of a pathogen or other organism can be detected indirectly by detecting the presence of byproducts given off by the microorganism during its growth. For example, certain microorganisms such as mammalian cells, insect cells, bacteria, viruses, mycobacteria and fungi consume oxygen during their growth and life cycle. As the number of microorganisms increases in the sample culture, they naturally consume more oxygen. Furthermore, these oxygen consuming organisms typically release carbon dioxide as a metabolic byproduct. Accordingly, as the number of organisms present increases, the volume of carbon dioxide that they collectively release likewise increases.
Several methods exist for measuring the increase of carbon dioxide in a sample to determine whether organisms are present in the sample. For example, an instrument known as the Bactec® 9050 manufactured by Becton Dickinson and Company detects changes in the color of an indicator to determine whether carbon dioxide is present in a sample. That is, each sample is collected in a respective sample vial containing an indicator medium having a chemical that reacts to color change in the presence of carbon dioxide. A light sensor then detects the color of the indicator medium in the sample vial when the sample vial is loaded into the instrument. If the sample contains an organism which emits carbon dioxide as a function of growth and/or metabolic activity, the reflected or fluorescent intensity of the indicator medium will change in response to the presence of the carbon dioxide. The light sensor will therefore detect this change in intensity, and the instrument will indicate to an operator that an organism is present in the sample contained in the sample vial. Other examples of instruments for detecting the presence of organisms in a sample by measuring the changes in carbon dioxide in the sample are described in U.S. Pat. Nos. 4,945,060; 5,164,796; 5,094,955 and 5,217,876, the entire content of each of these patents being incorporated herein by reference.
Alternatively, instead of measuring the presence of carbon dioxide to detect the presence of an oxygen consuming microorganism, it is possible to measure depletion in the concentration of oxygen in the sample of interest. In such a system, the sample vial includes an indicator whose color or fluorescence changes as the concentration of oxygen in the vial changes. This change in color or fluorescence can be detected by an instrument, which can provide an indication to a technician that oxygen in the sample is being depleted by an oxygen consuming organism within the sample. An instrument employing such an oxygen detecting technique is described in U.S. Pat. No. 5,567,598, the entire content of which is incorporated herein by reference.
The presence of oxygen consuming organisms can also be detected by measuring a change in the pressure in a sealed sample vial containing the sample of interest. That is, as oxygen in a closed sample vial is depleted by oxygen consuming organisms, the pressure in the sealed sample vial will change. The pressure will further change in the sample vial as the organisms emit carbon dioxide. Therefore, the presence of such organisms can be detected by monitoring for changes in the pressure in the closed sample vial. Instruments that are capable of detecting such changes in pressure in the sample vial are described in U.S. Pat. Nos. 4,152,213; 5,310,658; 5,856,175 and 5,863,752, the entire content of each of these patents being incorporated herein by reference.
While existing technology is effective, improvements are always desirable.